This invention relates to ablative burrs for medical procedures and, in particular, to an ablative burr for performing an atherectomy procedure.
A number of vascular diseases, such as atherosclerosis, medial sclerosis, arteriolosclerosis, and thrombosis are characterized by the buildup of deposits (atheromas), clots, or growths in or on the intimal layer of a patient""s blood vessels. Such deposits generally result in occlusions in a person""s vascular system that can impede the flow of blood to the affected portion of the person""s body. If the occlusion is not removed or otherwise ameliorated, enlargement of the occlusion can result in the complete stoppage of blood flow to the affected region. This can be particularly serious, of course, if the occlusion occurs in a portion of the vasculature that supplies vital organs with blood or other.necessary fluids.
To treat such diseases, many invasive and noninvasive techniques and therapies have been developed. For example, cardiac bypass surgery is now a commonly performed procedure wherein an occluded cardiac artery is bypassed with a segment of a healthy blood vessel that is obtained from elsewhere in the body. While this procedure is frequently successful, it is extremely traumatic to the patient because the entire chest cavity must be opened to access the site of the occluded artery. Because of the trauma and substantial risks associated with cardiac bypass surgery, this procedure may not be a viable option for certain patients, particularly for elderly or relatively frail patients.
As an alternative to cardiac bypass surgery, numerous atherectomy (atheroma removal) devices have been developed for removing such deposits in a less invasive manner. One such device that is particularly suited to removing calcified atherosclerotic plaque is an ablative rotational atherectomy device, such as that disclosed in U.S. Pat. Nos. 4,990,134 and 5,314,407, both to Auth. Auth teaches using a small burr covered, or partially covered, with an abrasive cutting material, such as diamond grit. The burr is attached to the distal end of a flexible, rotatable drive shaft that can be slidably inserted over a guide wire that is inserted through the vasculature of a patient to the site of an occlusion. A rotational atherectomy device practicing the Auth invention is sold by the assignee of the present invention under the trademark Rotablator(copyright) and is described below.
Refer now to FIG. 1, depicting the Rotablator ablative rotational atherectomy device 10. This prior art device utilizes a guide wire 26 that is inserted through the patient""s vasculature approximately to the location of the deposit that is to be treated. A hollow, flexible drive shaft 22 having an ablative burr 24 at its distal end is then inserted over the guide wire 26, and advanced to a location just proximal to the deposit. The drive shaft 22 is covered with a lumen or catheter 20 along most of its length to minimize the impact to surrounding tissue when the drive shaft 22 is rotatably engaged. The drive shaft 22 is connected to a compressed-air driven drive assembly 16 having a turbine (not shown) that can rotate the drive shaft 22 at relatively high rotational speeds. The drive assembly 16 is slidably mounted in an advancer housing 12 on a track, allowing a surgeon using the Rotablator device 10 to move the drive assembly 16 transversely, and hence move the drive shaft 22 and burr 24 forward and backward to impact and ablate the atheroma.
Rotational ablative atherectomy devices such as the Rotablator(copyright) have proven to be effective in treating various types of atheroma. Use of the device, however, requires that a guide wire, drive shaft, and catheter be inserted into the patient and maneuvered through the patient""s vasculature to the site of the deposit. It is desirable to minimize the diameter of the catheter in order to facilitate insertion of the device through the patient""s vasculature. The minimum diameter of the catheter, however, is limited by the diameter of the drive shaft. The drive shaft, extending from outside the patient up to the atherectomy burr, is then driven externally to provide the driving force to the burr for performing the ablative atherectomy procedure. The patient""s vasculature may follow a tortuous path between the point of insertion of the drive shaft and the situs of the atheroma. The drive shaft must be very flexible to negotiate such tortuous path. Moreover, rotation of the in situ drive shaft may generate undesirable stresses on the patient""s vasculature.
It would be beneficial to reduce the diameter of the catheter that must be inserted through the patient""s vasculature and, in particular, to eliminate the drive shaft that drives the burr.
The present invention overcomes many of the disadvantages of the prior art by providing an ablation burr that does not require the insertion and operation of a flexible drive shaft through the vasculature of the patient to the sight of the occlusion. The ablation burr according to the present invention utilizes a two-piece burr having a rearward piece attached to a small catheter and an abrasive forward piece elastically connected to the rearward piece. Oscillatory drivers are provided between the forward and rearward pieces that force the forward piece to oscillate. By forcing the forward piece at a resonant frequency, relatively large amplitude oscillatory motion of the forward piece can be achieved.
In an embodiment of the present invention, an ablative burr includes a main body member, a shell member longitudinally coupled to the main body member, and an oscillatory driver disposed between the main body member and the shell member that is adapted to vibrate the shell member at a predetermined frequency. The main body member includes a narrow proximal portion that is attachable to a catheter, an aft-body portion and a coaxial distal portion. The shell member extends around the distal portion and is longitudinally and elastically restrained by the main body member.
In an embodiment of the invention, the oscillatory driver includes an annular piezoelectric transducer that is situated between the main body member and the shell member, and oscillates the shell member longitudinally at a resonant frequency of the shell member.
In another embodiment of the invention, the oscillatory driver includes a plurality of annular piezoelectric transducers that are coaxially stacked with electrode plates therebetween, to produce a cumulative forcing amplitude.
In an aspect of the invention, flexible annular washers are provided between the main body member and the shell member.
In another embodiment of the invention, the oscillatory driver includes at least one elongate piezoelectric transducer situated between the main body member and the shell member, and oscillates the shell member rotationally about its axis at a resonant frequency of the shell member.
In another embodiment of the invention, the oscillatory driver includes a plurality of elongate piezoelectric transducers that are stacked side by side with electrode plates therebetween, to produce a cumulative forcing amplitude.